WATER TRANSPARENCY OBSERVATIONS 



ALONG THE EAST COAST OF 



NORTH AMERICA 



By JEROME WILLIAMS, E. R. FENIMORE JOHNSON AND 

 ALBERT C. DYER * 



(With 2 Plates) 



INTRODUCTION 



Marine biologists have long been interested in the transparency of 

 natural waters as an important parameter in the determination of 

 both the amount and type of plant life at various depths. Owing to 

 this interest, many transparency surveys, in the oceans [4, 8, 16, 19, 

 22, 23], 2 in lakes [7, 33], and on pure water [27], have been made. 

 In recent years, however, this interest in water clarity has spread to 

 other fields, such as underwater photography (1, 9, 20, 24, 33) and 

 television. In addition, there is a growing movement among workers 

 in the field to utilize transparency as a "tag" for water masses in the 

 study of such things as circulation patterns [23, 25]. 



During the years 1947-51 the yacht Elsie Fenimore made a rather 

 extensive survey of water transparency conditions along the east coast 

 of North America from Labrador to the Gulf of Mexico, including 

 some stations around Newfoundland and the British West Indies. 

 Even though the data herein presented are admittedly far from com- 

 plete and a number of other studies have been made of the area [3, 

 5, 10, 11, 12, 13, 14, 15, 17, 18, 21, 28, 31] this study represents, from 

 a geographical standpoint, the most extensive single piece of work 

 done on the subject to date. For this reason, if for no other, it seems 

 desirable to publish this information in the present form so that it 

 may become available. 



To make the data as universal as possible the unit chosen was the 

 so-called Equivalent Secchi Disc Reading. Since it is obviously im- 

 possible to use the Secchi Disc [32] for measurement of water trans- 

 parency if the water mass to be measured is at a great depth, this 

 water mass is hypothetically brought to the surface for measurement. 

 Thus the Equivalent Secchi Disc Reading may be said to be the dis- 



1 Mr. Williams is associated with the Chesapeake Bay Institute ; Mr. Johnson 

 is a research associate in the Limnology Department, Academy of Natural 

 Sciences of Philadelphia; and Mr. Dyer is connected with the Fenjohn Company. 



2 Numbers in brackets indicate references in the bibliography. 



SMITHSONIAN MISCELLANEOUS COLLECTIONS, VOL. 139, NO. 10 





